The present invention relates to an apparatus for promoting the vaporization of liquid fuel in an internal combustion engine.
The low engine temperature before completion of the engine warm-up results in insufficient vaporization of the fuel supplied from the carbureter. The supply of a large quantity of fuel into the engine cylinders in the liquid state results in poorer combustion than after completion of the warm-up, so that a stable operation of the engine cannot be obtained. Accordingly, during the warm-up, an air-fuel mixture, which is richer than the air-fuel mixture used after completion of the warm-up, is supplied into the engine cylinders so as to maintain a stable engine operation. However, the supply of such a richer air-fuel mixture to the engine cylinders causes not only an increase in the amount of poisonous components, such as unburnt hydrocarbons HC and carbon monoxide gas CO in the exhaust, but also an increase in the fuel consumption. Accordingly, sufficient vaporization of the liquid fuel supplied from the carbureter during the engine warm-up would enable a stable engine operation, even with a reduced air-fuel mixture. The use of such a reduced air-fuel mixture would allow the control of the formation of poisonous components in the exhaust gas and the reduction of the fuel consumed. We previously proposed an intake heating apparatus for promoting vaporization of a liquid fuel during the engine warm-up, which comprises a hollow heating element vessel attached to, for example, the outlet portion of a carbureter air horn, said hollow heating element vessel including an inner pipe, an outer pipe, and a plurality of positive temperature coefficient thermistors (hereinafter referred to as "PTC elements") inserted between the inner and outer pipes, wherein the inner pipe of the hollow heating element vessel is heated by heating the PTC elements (c.f. Japanese patent application Nos. 55-169050 and 56-157536.)
In such an intake heating device utilizing PTC elements, it is necessary that the intrusion of various materials, such as fuel, oil, water, dust or the like, be prevented. On the other hand, PTC elements themselves always need fresh air in order to maintain their fundamental function; otherwise, the life of the PTC elements will be shortened due to changes of the characteristic curve.